The field of this invention is cheese making and more particularly to a composition and method for propagating a starter culture suitable for use with high solids content milk.
Traditionally, cheese is manufactured from milk consisting of approximately 13% solids and 87% water. Approximately 3.5% of the solids in milk is protein. During cheese manufacture, as a result of the combined action by added enzymes and starter cultures, a large portion of this protein (casein) is precipitated from solution and is mechanically and microbiologically transformed into what we call cheese of many varieties. However, a significant portion of the milk protein (whey proteins) remain in the fluid phase of cheese manufacture (whey) along with other soluble solids such as lactose.
Traditional propagation of bulk starter culture used as one of the principle cheese making ingredients is conducted in a growth medium made up of dairy-derived ingredients such as milk and/or whey solids and various food-grade chemicals. A typical conventional bulk starter medium is described in U.S. Pat. No. 4,402,986 which description is incorporated herein in its entirely by reference.
Culture media generally range from 6-12% total solids. During traditional cheese manufacture the added solids in the form of bulk starter culture are mostly soluble in the whey portion and are not recovered as cheese. Therefore, the use of bulk starter culture is a direct expense in the process of manufacturing cheese.
In more recent times, the technology of membrane separation has been applied to cheese making to radically change this traditional process. The general approach in ultrafiltration cheese making has been to separate whole milk into cream and skim milk and then to subject the skim milk to ultrafiltration concentration and then to recombine the cream with the ultrafiltered concentrate, called retentate. This liquid "precheese" is then inoculated with culture and then set with rennet for conversion to cheese curd. Using the separation techniques of ultrafiltration and reverse osmosis, the solids in milk can be selectively separated and concentrated prior to the fermentation of milk into cheese. As a result of this process all of the protein including casein and whey proteins are recovered as cheese, making this form of manufacture more efficient and profitable. As opposed to traditional cheese making, the added solids in the form of bulk starter culture are generally recovered as cheese solids.
In ultrafiltration processes the concentrated form of milk, herein referred to a retentate, generally consists of up to about 40% total solids. This high concentration of solids introduces new problems to the role of the starter culture in cheese making. The primary role of the cheese starter culture is to produce sufficient lactic acid as a result of the fermentation of milk lactose to reduce the pH of the cheese to approximately 5.0. The high solids of the retentate results in a more inhibitory growth environment for the starter culture that normally is grown in milk at 13% solids; possibly as a result of the higher osmotic pressure provided by the additional solids. In addition, the solids in the retentate produce a greater buffering capacity making it more difficult to effectively reduce the pH to the desired level. These effects require a longer processing time and therefore reduces the economic attractiveness of the ultrafiltration cheese making process. Attempts to shorten the processing time have included increasing the amount of starter inoculum. This, however, dilutes retentate protein thereby lowering the yield gain from the use of ultrafiltration.
Also, salt, which is normally added at the end of traditional cheese making fermentation to arrest the action of the starter culture, is sometimes added to the retentate before the cheese making fermentation, making the retentate even more inhibitory to growth by traditional starter cultures.
An objective of the present invention is the provision of a method of producing a starter culture inoculum suitable for use in cheese making, employing high solids content ultrafiltration retentate.
It is also an objective of the present invention to provide a bulk starter culture which will function in high solids content retentate to produce a cheese product.
It is a further objective of the present invention to provide an improved ultrafiltration method of cheese making wherein a starter culture is utilized which is not inhibited by the high solids content of milk retentate.
It is yet a further objective of the present invention to provide a growth medium which will produce a bulk starter culture that functions in high solids content retentate while retaining high yields.